This year, a third, or 16, of the 46 American service members killed in Afghanistan have died at the hands of Afghan security forces, including Monday when a man alleged to be a local Afghan police officer killed an American service member in eastern Afghanistan.

Gen. John Allen, the commander of the NATO-led force, said officials are working on a new procedure to check the background of Afghans who sign up to join the security services.

The latest killings come after a shooting rampage in Afghanistan this month left 17 villagers dead in the Panjwai district of southern Kandahar province. A U.S. soldier, Staff Sgt. Robert Bales, has been charged with murder.